I always have certain staples on hand that I can use for unexpected guests, although it doesn’t happen frequently. They are pretty much the same staples I have on hand for snacks or a last minute family meal. For snacks, I would put out cheeses and crackers along with whatever fruit I have on hand.  If I had to make a last minute meal, I would make a simple pasta dish or a quick frittata with vegetables (fresh or frozen) or anything else hanging out in my pantry. Here are some examples of what pastas I might make:

• pasta with zucchini (or other veggies) and garlic sautéed in olive oil and finished with freshly grated parmesan
• pasta with any veggies mixed with chopped sun-dried tomatoes
• pasta with cherry tomatoes, olives, and canned cannellini beans

A cheese, fruit, and nut platter is my go-to offering for short-notice visits.  I usually use a large cutting board to present a assortment of whatever cheeses I have on hand, dried fruits, and almonds or walnuts or pistachios (often putting the nuts in a small bowl to keep them separate in case of nut allergies).  I also offer bowls of pretzels, crackers or sliced baguette (which I keep in the freezer and can defrost and toast quickly).